Method of synthesizing zirconium-loaded fibrous adsorbent materials having phosphoryl groups and removal of objectionable substances using the adsorbents

ABSTRACT

A zirconium-loaded fibrous adsorbent material having phosphoryl groups which is produced by first grafting a reactive monomer having phosphoryl groups onto a polymeric substrate and then loading zirconium.

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2002-358915 filed Dec. 11, 2002, theentire contents of this application are incorporated herein byreference.

BACKGROUND OF THE INVENTION

This invention relates to an adsorbent material for recovering andremoving objectionable substances, in particular, arsenic that arecontained in environmental water and liquid wastes such as waste waterfrom plants. The invention also relates to a method of synthesizing theadsorbent material.

Research and development efforts have recently been made on materialscapable of trapping metals contained in environmental water bodies suchas rivers and the sea and this has led to the discovery that cationexchange resins using phosphoric acid as exchange groups can adsorbmetal ions present in rivers, lakes and wastewater from plants (see, forexample, Akinori Joh et al., “Cation exchange resins using phosphoricacid as exchange groups—Their selectivity for metal ions andapplications” in PHOSPHORUS LETTER, Japanese Association of InorganicPhosphorus Chemistry, Feb. 1, 2001, vol. 40, pp. 16-21).

Further, the present inventors developed a metal adsorbent material thathad a monomer with phosphoryl groups grafted onto a polymeric substrate(see, for example, Japanese Patent Application No. 2002-262502).

In the art of recovering and removing objectionable substances in theenvironment, particularly arsenic, two major methods have so far beenpracticed, one relying upon coagulating sedimentation and the otherusing chelating resins (see, for example, Xiaoping Zhu et al., “Removalof arsenic(V) by zirconium(IV)-loaded phosphoric acid chelating resin”in “SEPARATION SCIENCE AND TECHNOLOGY”, America, Marcel Dekker, Inc.,2001, 36(14), pp. 3175-3189).

However, the conventional adsorbent materials can adsorb arsenic onlyslowly. If arsenic is recovered and removed by coagulating sedimentationor with the aid of adsorbent materials in bead form, considerableinconvenience in handling has been met during the process of removal orin subsequent operations.

In addition, the conventional arsenic adsorbent materials are mostlysynthesized by common radical polymerization and their structure foradsorption of arsenic is so unstable that it is prone to leak out evenif it is adsorbed.

According to the Basic Environment Law which provides for the waterquality guidelines for public waters, arsenic should not be dischargedat concentrations higher than 0.1 ppm and its content in the environmentshould not exceed 0.01 ppm. Thus, the removal of arsenic is absolutelynecessary.

SUMMARY OF THE INVENTION

An object, therefore, of the present invention is to provide anadsorbent material that allows for faster adsorption of arsenic andanion such as phosphoric ion and which can remove them even if they arepresent at extremely low concentrations.

Another object of the invention is to provide an adsorbent material thatis easy to handle during or after adsorptive removal of arsenic andwhich is capable of efficient adsorption of arsenic.

In order to attain those objects, the present inventors made intensivestudies and completed the present invention which relates to azirconium-loaded fibrous adsorbent material having phosphoryl groups.

The zirconium-loaded fibrous adsorbent material of the invention havingphosphoryl groups is produced by first grafting a reactive monomerhaving phosphoryl groups onto a polymeric substrate and then loadingzirconium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the pH dependency of the performance of thezirconium-loaded adsorbent material of the invention in adsorbingarsenic;

FIG. 2 is a graph showing the dependency on flow rate of arsenicadsorption by the zirconium-loaded adsorbent material of the invention;and

FIG. 3 is a graph showing the dependency on arsenic's concentration ofthe zirconium-loaded adsorbent material of the invention.

FIG. 4 is a graph showing the phosphoric ion adsorption characteristicsof the adsorbent material of the invention.

FIG. 5 is a breakthrough curve of phosphoric ion on the adsorbentmaterial of the invention.

FIG. 6 is a breakthrough curve of fluoride ion on the adsorbent materialof the invention.

DETAILED DESCRIPTION OF THE INVENTION

The adsorbent material of the invention is a zirconium-loaded fibrousadsorbent material having phosphoryl groups and it is produced by firstgrafting a reactive monomer having phosphoryl groups onto a polymericsubstrate and then loading zirconium.

In the invention, fibers of polypropylene, polyethylene, polyester orcomposites thereof can be used as the polymeric substrate and they maytake on various forms including short fiber, filament, nonwoven fabricor woven fabric.

The first step in the synthesis of the adsorbent material of theinvention is preparing an adsorbent precursor (hereunder sometimesreferred to as the “graft product”) by grafting a reactive monomerhaving phosphoryl groups onto the polymeric substrate.

1. Preparing the Adsorbent Precursor (Graft Product)

The method for preparing the graft product may comply with theconditions for synthesis disclosed in Japanese Patent Application No.2002-262502. Specific procedures and conditions of the method aredescribed below.

A monomer having mono- or difunctional phosphoryl groups may beintroduced into the polymeric substrate and specific examples include:

-   mono(2-methacryloyloxyethyl)acid phosphate    CH₂═C(CH₃)COO(CH₂)₂OPO(OH)₂;-   di(2-methacryloyloxyethyl)acid phosphate    [CH₂═C(CH₃)COO(CH₂)₂O]₂PO(OH);-   mono(2-acryloyloxyethyl)acid phosphate CH₂═CHCOO(CH₂)₂OPO(OH)₂;-   di(2-acryloyloxyethyl)acid phosphate [CH₂═CHCOO(CH₂)₂O]₂PO(OH); and-   mixed monomers thereof.

In the case of using mixed monomers, the mixing ratios of the respectivemonomers may be changed appropriately.

A type of monomer having the following structure may also be used as thereactive monomer:CH₂═C(CH₃)COO(CH₂)_(l)OCO—R—CO—OPO(OH)R′,wherein R is an optionally substituted (CH₂)_(m) or C₆H₄; R′ is ahydroxyl group or CH₂═C(CH₃)COO(CH₂)_(n)OCO—R—CO—O— group; l, m and nare each independently an integer of 1-6.

Graft polymerization can be effected by first generating reaction activepoints in the polymeric substrate and then bringing it into contact withthe reactive monomer.

Reaction active points can be generated by either one of the followingmethods (a)-(c).

(a) Exposure to Radiation

The polymeric substrate as preliminarily nitrogen purged is exposed toradiation in a nitrogen atmosphere either at room temperature or undercooling with Dry Ice. The radiation to be employed is electron beams orγ-rays. The exposure dose may be determined appropriately on thecondition that it be sufficient to generate reaction active points andit is typically in the range of 50-200 kGy.

(b) Exposure to Plasma

The polymeric substrate as preliminarily nitrogen purged is exposed toplasma in a nitrogen atmosphere at room temperature. The exposurecontinues for 1-24 hours using rf waves at 10 MHz or higher.

(c) Use of Initiator

Under nitrogen bubbling, reaction active points are generated using aradical initiator at between room temperature and 50° C. Exemplaryradical initiators include azobisisobutyronitrile and benzoyl peroxide.

While graft polymerization can be effected in a nitrogen atmosphere, theconcentration of oxygen in the atmosphere is preferably low in order toachieve higher values of percent grafting. The term “percent grafting”as used herein means the ratio in weight percentage of the reactivemonomer to the polymeric substrate onto which it has been grafted. Thereaction temperature which depends on the reactivity of the reactivemonomer is generally between 40 and 60° C. The concentration of themonomer suffices to range from 10 to 30% of the solvent. The reactiontime which is generally 1-48 hours can be determined depending upon thereaction temperature and the percent grafting required.

2. Synthesis of the Zirconium-Loaded Adsorbent Material

The adsorbent material of the invention can be produced by loading thethus prepared graft product with zirconium.

The graft product is subjected to passage of a zirconium compound insolution at a pH of 0.5-2 for 1-24 hours at a flow rate of 100 mL/h. Thezirconium compound that can be used in the invention is a zirconium(IV)compound, a zirconium(III) compound or a zirconium(II) compound and maybe exemplified by zirconic acid, zirconate (a conventional oxo-acid saltof zirconium(IV)), zirconate (which is not an oxo-acid of zirconium),etc. Specific examples of zirconium compounds in solution includesolutions of zirconium nitrate, zirconium sulfate, zirconium chlorideand zirconium oxide, as well as an analytical standard solution ofzirconium. The concentration of zirconium compounds in solution can beadjusted appropriately.

In order to subject the graft product to passage of zirconium compoundsin solution, any means known to the skilled artisan may be employed,such as stirring the solution in which the graft product is immersed orpassing the solution through a column packed with the graft product.Preferably, the desired product can be obtained by stirring 10 mmol/L ofzirconium nitrate in solution at a pH of 1 for one hour as it containsthe graft product immersed therein or by passing the solution through acolumn packed with the graft product.

The arsenic adsorption characteristics of the adsorbent material of theinvention are depicted in FIGS. 1-3.

FIG. 1 is a graph showing the pH dependency of arsenic adsorption atvarying pHs of an arsenic containing liquor. As one can see from FIG. 1,the adsorbent material of the invention can adsorb arsenic at pHs of 1-9and its adsorbing capability is by no means dependent on pH. It can alsobe seen that the difference in absorbing capability is particularlysmall in the acidic range below pH=7. At each of the tested pH values,the absorbing capability of the adsorbent material saturated andsubstantially leveled off when the amount of the effluent was about 130times the volume of the sample.

FIG. 2 is a graph showing the dependency on flow rate of arsenicadsorption at varying flow rates of an arsenic containing liquor. As onecan see from FIG. 2, the adsorbing capability was maintained when thearsenic containing liquor was passed at space velocities of 64-1300 1/hand this indicates that arsenic could be adsorbed without leakage evenat high treatment speeds. The data in FIG. 2 shows the feasibility ofthe adsorbent material of the invention in large-scale, high-speedtreatments as in plants.

FIG. 3 is a graph showing the concentration dependency of arsenicadsorption at varying concentrations of arsenic in an arsenic containingliquor. As one can see from FIG. 3, the adsorbing capability of theadsorbent material of the invention does not vary much at arsenicconcentrations of 1-5 mmol/L and can be maintained independent of theconcentration of the treating liquor.

Thus, FIGS. 1-3 show that the adsorbent material of the inventionexhibits high adsorbing capability independent of the concentration ofthe treating liquor, the pH and the treating speed.

The following examples are provided for further illustrating the presentinvention but are in no way to be taken as limiting.

EXAMPLE 1

A nonwoven fabric as a polymeric substrate was subjected to graftpolymerization and the resulting graft product in nonwoven fabric formwas rendered wet by passing pure water. In the process of preparing thegraft product, the conversion (the degree of grafting) was 100-400% andphosphoryl groups were introduced in amounts of 4-8 mmol/g.Subsequently, the graft product was packed into an adsorption column,through which an aqueous solution of zirconium nitrate (10 mmol/L, pH=2)was passed for one hour at a flow rate of 100 mL/h so as to load thegraft product with zirconium. Thereafter, the column was washed withpure water until the pH of the effluent was between 5 and 7, therebyyielding a zirconium-loaded adsorbent material. The zirconium loadingwas 4.2 mmol/g. The adsorbent material produced in Example 1 using thenonwoven fabric is not only usable as a filter on its own; the scope ofits applications can be widened by processing it into various shapes ormaking a laminate of it.

EXAMPLE 2

Polyethylene short fiber was used as a polymeric substrate, onto which areactive monomer having phosphoryl groups was grafted to prepare a graftproduct. The degree of grafting was 100-300% and phosphoryl groups wereintroduced in amounts of 1-8 mmol/g. An aqueous solution of zirconiumpreliminarily adjusted to 10 mmol/L was treated with nitric acid to havea pH of 1. The fibrous graft product was immersed in that acidic aqueoussolution of zirconium, which was then stirred for 1-24 hours at 25° C.The zirconium-loaded adsorbent material was obtained and it was found tohave zirconium introduced in an amount of 4.0 mmol/g.

The adsorbent material produced in Example 2 using the short fiber hasgood processability and can be packed into various types of modulesincluding columns, thus expanding the scope of its applications.

The adsorbent material of the present invention is synthesized byutilizing graft polymerization, so a crosslinked structure can be easilyformed within the adsorbent material. Since this facilitatesimmobilization of zirconium which is responsible for adsorbing arsenic,not only the arsenic contained in the environment such as natural waterbut also other objectionable substances including antimony andnegatively charged ions such as fluoride and chloride ions can be easilyremoved, thus adding potential uses including prevention ofenvironmental pollution and purification of potable water.

Unlike the conventional adsorbent materials that must be processed intomodules for practical use, the adsorbent material of the invention canbe directly used as a filter and permits easy handling.

EXAMPLE 3

The phosphoric ion adsorption characteristics of the adsorbent materialof the invention are depicted in FIG. 4. It was depicted by subjectingthe material to a passage of phosphoric ion containing liquors at a pHof 1.5 having various phosphoric ion concentrations at varying contacttime. Compared with the prior method of adsorbing phosphoric ions byusing a zirconium-loaded activated carbon, the rate of adsorptionobtained by the adsorbent material of the invention is so high that thepercentage of adsorption attained up to about 100% in 2 hours.

The breakthrough curve of phosphoric ion on the adsorbent material ofthe invention was depicted in FIG. 5. As shown in FIG. 5, when theadsorbent material of the invention was packed into a column, throughwhich a phosphoric ion containing liquor was passed, no phosphoric ionwas leaked independent of the phosphoric ion concentration in theliquor.

EXAMPLE 4

Adsorption experiment was conducted on the adsorbent material of theinvention by using a fluoride ion containing liquor. The liquor wasprepared by adjusting pH of a standard solution of fluorine (10 mmol) to7. The breakthrough curve of fluoride ion on the adsorbent material wasdepicted in FIG. 6. The adsorbent material of the invention was packedinto a column, through which the liquor was passed at flow rate of 1300h⁻¹, 240 h⁻¹, and 64 h⁻¹, in result, the breakthrough point was about 50independent of the flow rate of the liquor.

1. A zirconium-loaded fibrous adsorbent material having phosphorylgroups which is produced by first grafting a reactive monomer havingphosphoryl groups onto a polymeric substrate and then loading zirconium,wherein the zirconium-loaded fibrous adsorbent material has a zirconiumcontent in an amount of 4.0 or 4.2 mmol/g.
 2. The zirconium-loadedfibrous adsorbent material of claim 1, wherein the fibrous material isselected from the group consisting of a fiber, a filament, a nonwovenfabric or a woven fabric.
 3. The zirconium-loaded fibrous adsorbentmaterial of claim 2, wherein the fiber is a fiber of polypropylene,polyethylene or polyester.
 4. The zirconium-loaded fibrous adsorbentmaterial of claim 3, wherein the fiber is a fiber of polypropylene, orpolyethylene.
 5. The zirconium-loaded fibrous adsorbent material ofclaim 1, wherein the phosphoryl group is a member selected from thegroup consisting of mono(2-methacryloyloxyethyl)acid phosphate,di(2-methacryloyloxyethyl)acid phosphate, mono(2-acryloyloxyethyl)acidphosphate, di(2-acryloyloxyethyl)acid phosphate, and mixtures thereof.6. The zirconium-loaded fibrous adsorbent material of claim 1, whereinthe reactive monomer comprises a material of formula:CH₂═C(CH₃)COO(CH₂)_(l)OCO—R—CO—OPO(OH)R′ wherein R is an optionallysubstituted (CH₂)_(m) group or C₆H₄ group, wherein R′ is a hydroxylgroup or a CH₂═C(CH₃)COO(CH₂)_(n)OCO—R—CO—O— group, wherein l, m and nare each independently an integer of 1-6.
 7. The zirconium-loadedfibrous adsorbent material of claim 1, wherein the fibrous material is afilter.